1. Field of the Invention
The present invention relates to an organic light emitting element comprising an anode, a cathode and a layer containing an organic compound that can obtain light emission when an electric field is applied thereto (hereinafter referred to as an “organic compound layer”, an “electroluminescent layer” or an “EL layer”), and a light emitting device using such an organic light emitting element. For example, the invention relates to an electronic apparatus mounting as its component a light emitting device that includes an organic light emitting element.
Note that the light emitting device in this specification refers to an image display device, a light emitting device or a light source (including a lighting system). In addition, a module where a connector such as a Flexible Printed Circuit (hereinafter referred to as a FPC), a TAB (Tape Automated Bonding) tape and a TCP (Tape Carrier Package) is attached to a light emitting device, a module where an end of a TAB tape or a TCP is provided with a FPC, and a module where ICs (Integrated Circuits) are directly mounted on light emitting elements by COG (Chip On Glass) bonding all fall within the category of the light emitting device.
2. Description of the Related Art
In recent years, researches of a light emitting device using an EL element as a luminous element have been actively developed and in particular, a light emitting device using an organic material as an EL material is attracting attentions. Such a light emitting device is also referred to as an EL display.
Note that the EL element comprises an anode, a cathode and an organic compound layer (EL layer) that is capable to generate luminescence (Electroluminescence) when an electronic field is applied thereto.
Since a light emitting device is a luminous type unlike a liquid crystal display device, it has no problems concerning the viewing angle. That is, it is more suitable for outdoor use than a liquid crystal display, and uses of various styles thereof have been proposed.
An EL element has a structure where an EL layer is sandwiched by a pair of electrodes, and the EL layer generally has a stacked-layer structure. Typically, a sequentially stacked-layer structure of “a hole transporting layer, a light emitting layer, and an electron transporting layer” is employed. This structure can provide quite high luminous efficiency, and is adopted for most of the light emitting devices that are under research and development currently. It is said that an EL element can emit light when an electric field is applied to a pair of the electrodes that sandwiches an organic compound layer, which causes electrons injected from the cathode and holes injected from the anode to be recombined in the luminescence center of the organic compound layer to form molecular excitons, and the molecular excitons release energy in returning to the ground state, and then emit a light. As an excited state, an excited singlet state and an excited triplet state are known, and it is considered that light emission can be obtained through either of the excited states.
In addition, a light emitting element formed of a cathode, an EL layer and an anode is referred to as an EL element, and there are two types of a light emitting device that uses such an EL element: a light emitting device where an EL layer is formed between two types of striped electrodes that are provided crosswise (passive matrix method); and a light emitting device where an EL layer is formed between a pixel electrode that is connected to a TFT and arranged in matrix, and an opposite electrode (active matrix method). However, when the pixel density is increased, the active matrix method, in which a switch is provided per pixel (or per dot), is considered advantageous as it enables low voltage drive.
An EL material that forms an EL layer deteriorates quite easily resulting from oxidation or moisture absorption due to oxygen or moisture, which leads to a luminance decay or shorter life of the light emitting element.
Display devices having a structure against such deterioration of the EL element have been developed. There is a method in which EL elements are put in an airtight container to shut the EL elements in an airtight space and block out the outside air, and a drying agent is provided separately from the EL elements (see Patent Document 1, for example).
Alternatively, there is a method in which a sealant is formed on an insulator where EL elements are formed, and the airtight space, which is surrounded by a covering material and the sealant with the use of the sealant, is filled with a filling material to block out the outside air (see Patent Document 2, for example).
[Patent Document 1] Japanese Patent Laid-Open No. Hei 9-148066
[Patent Document 2] Japanese Patent Laid-Open No. Hei 13-203076
In order to advance reduction in manufacturing cost of a light emitting device, integral formation of a driver circuit and a pixel portion on a common substrate has been promoted.
When a pixel portion and a driver circuit for controlling the pixel portion are integrally formed on a common substrate, a frame portion that is the region other than the pixel region tends to occupy a larger area as compared to the case of mounting a driver circuit by TAB. In order to reduce the area of the frame portion, a circuit scale of the driver circuit is required to be reduced. In particular, a portable phone that incorporates a small-sized display panel with a screen size of 5 inches or less requires further reduction of the frame portion.